It has long been desirable to increase feed efficiency, weight gain, and lean tissue of swine. Work has been performed with carnitine to achieve certain of these results and some success has been achieved. G. L. Newton and K.D. Haydon reported in the 1986 University of Georgia Swine Report that feeding diets containing 0.95, 1.1 or 1.25% lysine, with or without 0.2% dl-carnitine HCl, to 28 day old nursery pigs had an effect on daily weight gains and feed efficiency. The pigs were fed a conventional diet containing 72.4% corn and 24.2% soybean meal with vitamin, mineral and antibiotic supplementation. The 1.1% lysine diet produced higher daily gains and improved feed efficiencies than the other diets. The effect on daily gain was significant throughout the study, while the effect on feed efficiency was significant for the first 4 days. There were also significant linear and curvilinear effects of lysine level on feed efficiency after 4 and 28 days. Carnitine did not have a significant effect on performance and did not alter the need for lysine. However, the results indicated the possibility of a greater response to supplemental lysine when nursery diets were also supplemented with carnitine. There were indications that post-weaning lag might be somewhat reduced in lighter weight pigs.
The results of two supplemental trials conducted to determine whether addition of carnitine to nursery diets would have an effect on post-weaning lag were reported in the 1987 University of Georgia Swine Report by G. L. Newton and K.D. Haydon. In the first trial, 144 pigs were fed simple corn-soy diets containing two levels of lysine and four levels of carnitine. For the other trial, 180 pigs 28 days of age were fed complex diets containing milk products and three levels of lysine and three levels of carnitine. When added to the simple diet, carnitine tended to produce an increase in feed intake during the first 4 days, which resulted in slightly better gains and feed efficiency at that time. When added to the complex diet, carnitine tended to increase food intake over the entire 20 day trial. Carnitine addition resulted in increased weight gains at 14 and 20 days.
Work with L-carnitine in connection with finishing pigs has also been conducted. U.S. Pat. Application, Ser. No 387,856, filed July 31, 1989, improved weight gain, feed efficiency, and reduction of back fat were observed.
In addition, efforts have been made to decrease postweaning "lag" which has become more of a problem as swine are weaned earlier and earlier. Research work has been directed towards a variety of nutritional programs for early weaned pigs (weaning from 14 to 21 days of age), including high nutrient-density diets (J.L. Nelssen, "High Nutrient-Density Diets for Weanling Pigs," Kansas State Universitv Swine Research Report is that the feed regimes described did not appear to increase the lean tissue growth.
It has been reported that swine from different genetic sources (genotypes) have different capacities for lean tissue growth and that its disposition is affected by the availability of amino acids. In a 1989 University of Kentucky Research Report in an article by T.S. Stahly et al., "Influence of Genetic Capacity for Lean Tissue Growth on the Amino Acid Needs of Pigs," it was noted that carcass leanness was improved as dietary lysine levels were raised in connection with pigs in the 40 to 240 pound range and that pigs with high lean growth potential had much higher growth performance and lean gain when the nutrient density of the diet was increased. These results indicated that some improvement in lean growth, through dietary manipulation, should be possible with all genotypes.